An industrial burner typically comprises a housing having a fuel inlet, an air inlet, a burner nozzle, and a discharge outlet. The housing also usually includes a combustion sleeve that extends downstream to the discharge outlet. Air and fuel enter a burner through their respective inlets and are mixed as they pass through the burner nozzle. At the discharge outlet there is an "ignition zone" where an igniter creates a spark which ignites the fuel/air mixture. Ideally, the ignition zone is located where the air to fuel mixture is optimal. In a common arrangement in industrial burners, one or more igniters extend through the housing and nozzle, into the ignition zone. The igniters extend along the length of the burner, parallel with the typical flow of air and fuel. Due to the wide array and sizes of industrial burners, the distance between the housing and ignition zone will vary a substantial amount. This distance can approach one meter in length in some industrial burners. Not only do industrial burners vary in size and shape, but also in their application. Thus an igniter may be required to fire once every five seconds or merely once a month, depending upon the particular application. Regardless of the size, shape or application of the industrial burner, the reliability of the spark is of key importance to ensure proper ignition at the desired time.
One prior art approach has been to provide non-self-grounding igniter in which the discharge electrode of the igniter is grounded to a separate metal post. The post is typically mounted to the nozzle or housing of the burner. Unfortunately, this type of igniter structure can result in unreliable sparking. It was easy for the discharge electrode and ground electrode to be separated too great a distance to permit sparking. For example, the distance between the igniter and the post could charge during handling or possibly during repair or maintenance of the burner. With this approach, the length of the spark gap inherently depends upon the proper placement of the igniter within the burner. Even then, slight bends in the rod could make the spark gap too wide or too narrow, or even cause direct contact between ground and discharge electrode which would in turn prevent formation of spark. These small differences in distance can have a significant impact on the reliability of spark creation which can prevent ignition and therefore failure of the burner.
In an attempt to overcome this problem, a self-grounding igniter was developed where the ground electrode is provided on the igniter itself. This igniter allowed for the spark gap to be fixed within rather tight tolerances, thereby obviating the drawbacks of the earlier igniters. The ground electrode of this igniter extends along the length of the igniter, back to the housing to provide the necessary ground. In order to prevent the metal rod from prematurely discharging into the ground electrode, insulating material also extends back to the housing, in order to provide an electrical barrier protecting against premature discharge.
Despite the improvement in spark reliability, this solution of the self-grounding igniter has had problems of its own. As noted above, the ignition zone is often deep within an industrial burner, resulting in igniters that may approach a meter in length. As such, these igniters tend to be rather expensive due to the amounts of raw materials required to manufacture the igniters. More importantly, these igniters are fragile and difficult to handle. The ceramic insulation of these igniters break occasionally during installation or replacement. The high fragility and fracture rate in turn requires additional care during assembly, installation and handling, and any resulting breakage will increase the maintenance cost of industrial burners.